Flight B/C

[coachchuckaahs]

Generally, tail tilt will help the circle at lower power (cruise), while rudder offset will help at higher torque (climb). In some cases (not that often for SO planes) left thrust will help with very high torque (launch in a high ceiling).

However, excessive wash in will counter the turn-inducing trim aspects, especially at low power.

Coach Chuck

[bjt4888]

Astro,

I am replying to your PM in the public forum as my reply will hopefully be helpful to other students and as my reply will not reveal any of your private data as we will be discussing the trim parameters that are public in the FF kit instructions. Good job recording data!

Per your logged data, your CG is at 2.7 cm - 2.9 cm forward of the rear wingpost. This is 1.0625"-1.14" fwd of rear post. The kit instructions recommend 1.1875" to 1.875" forward of rear post so your setting is likely oo far back for initial testing (I suspected this based upon the "wandering/nose light" character of your flight video). Your wing incidence is currently 4 mm or 0.157" and is within the kit recommended range of .14"-.19". However, I am wondering about your tailboom shim. It appears to be a stack of three pieces of 1/16" thick wood. As the tailboom taper is only 1/8", if your tailboom is basically in line with the motor stick, a 3/16" shim would give you negative incidence in the stabilizer which would add a little over one degree to the total decalage making the .157" of positive wing incidence too much. So, possibly, you have too much positive wing incidence if you also have some negative stab incidence. You'll have to measure this to verify as whether there is stabilizer (TB) negative incidence as this can't really be seen in the picture. Rudder offset at 0.6mm or 0.236" is per plan. Left wing twist/warp as the kit instructions calls it (this is more properly called "washin") is noted in your log as 0.6mm, which is 0.236". The kit recommendation is for .125" or 0.3 mm. The stabilizer tilt you indicate on your log is 0.7mm. The kit recommendation is 1.5cm tilt; right stab tip this much higher than the stab center (at the tailboom joint). This may seem like a lot of stab tilt, but a V-dihedral airplane with tip plates on the stabilizer will likely need a lot of turn setting.

So, your best bet is to increase stab tilt to the kit recommendation, double check decalage (esp. any negative inc. in stabilizer), cut left wing washin by 50%, and probably move the CG forward again and start with very low power flights. If you haven't had a chance to read the first document in each of the NFFS website "Building" and "Flying" tabs, please read these carefully too https://www.freeflight.org/science-olym ... resources/

Typically, it is not a good idea to make more than one trim change at a time, but in this case the three to four changes are all to basically to get the settings to match the kit manufacturers recommendations; which would be your best starting point. If you want to make one change at a time, I'd reduce the washin to 3 mm (or less; see if you can get it to roll left) first, then increase the stabilizer tilt to 1.5 cm (tip to stab center measure), then move the CG forward to at least 1.1875" fwd of rear post. And before all of this, verify the stabilizer negative incidence (if any) and possibly correct this to zero.

Have fun and great job starting so early.

Brian T

Thanks for the reply! I tested today with the intention of moving to slightly higher torques in an attempt to induce roll and moving the CG forward. I remeasured the CG last night and it turned out to be 2.3 cm in front of the rear wingpost instead of 2.7 after I had moved some clay up, so I must've either measured it wrong earlier or moved the CG backward - probably the former. I gained at least 10 seconds from moving the CG forward, and I think I overdid it on the last flight as the angle of incidence was looking pretty sharp. Don't know for sure though because people had started entering the gym and the air currents were disrupting the plane significantly. I plan on increasing stab tilt for a tighter circle - does it help make the plane more resistant to circle drift? - it was a noticeable problem this morning. As for washin, the behavior seemed to improve at higher torques so I'll leave it where it is for now in anticipation that it'll help me when I go full power (Initial torque is still at 0.4 oz-in). Could launching the plane tilted inwards also help induce roll? I remember doing the opposite last year to counteract the inward roll. Flight log should still be accessible so you can see what I have, I'll upload the videos tomorrow.

Astro,

I have reviewed you log and it looks like good progress. A suggestion; start winding the motor fully. All of your logged flights show less than 70% max turns. Wind to at least 80% and 85%-90% would be better still at this point in your testing. Once you have a couple of low power flights in and have made any trim corrections to get safe, reasonable circles and gentle climb, you really will only make progress to best possible flights if you wind to 80-90% max turns and backoff to launch torque that gets desired climb height.

Have you had a chance to read the material on the NFFS website under the "Flying" tab yet, here: https://www.freeflight.org/science-olym ... resources/

Read the "Start here first, Basic Trimming Article". This is a new for 2023-24 3-page step by step trimming write up with links to a rubber winding demo showing me winding a motor for this year's rules. Also included in this article is a rubber motor max turns calculator that you can download to your phone and use while in the gym. This is the exact calculator that my teams use. After your first few flights, you could be at Step #7 in this instructional and getting at least another 15-20 seconds of flight time (unless the blowers in your gym are too big of a problem).

Keep up the good work!

Brian T

[Astronomyguy]

I've read all of the NFFS Flying section materials and have added RPS to my flight log. Most of my flights have been over 7.5 rps due to being not trimmed well or being disturbed by significant air currents, but I've had two exceptions - one at 5.9 and another at 6.1 RPS. Both of those flew well. One thing I noticed was that two flights that I previously thought were very similar (Flights 7 & 8 with times of 1:24 and 1:29 respectively) had drastically different RPS values of 7.7 and 6.1, only from a change in CG and decalage. I'm starting to think that this could be a useful indicator of how well your flights are doing and which ones to scale up to full torque - before, I wouldn't have been able to tell which settings between Flight 7 and Flight 8 to stick with as my trim (obviously both of them aren't optimized and I'm still in the trimming process) but now I know that Flight 7 was much more inefficient.

I'm also in the process of rechecking my plane configuration ahead of a potential extended session tomorrow and I found that my HS tilt and wing warp have changed from me carrying the plane back and forth from the school. My wing warp increased from 0.6 cm to 1.1 cm (nearly 4x the recommended value) and my HS tilt from 0.7 cm to 1 cm. Is there any way I can prevent these from changing so much besides being more gentle with the plane? Am I not putting enough glue on the joints?

I've added the videos for my latest flights if the coaches want to check them out. Planning to fly at full torque tomorrow and potentially moving to different rubber densities.

Thanks for all the help so far,
Astro

[bjt4888]

I've read all of the NFFS Flying section materials and have added RPS to my flight log. Most of my flights have been over 7.5 rps due to being not trimmed well or being disturbed by significant air currents, but I've had two exceptions - one at 5.9 and another at 6.1 RPS. Both of those flew well. One thing I noticed was that two flights that I previously thought were very similar (Flights 7 & 8 with times of 1:24 and 1:29 respectively) had drastically different RPS values of 7.7 and 6.1, only from a change in CG and decalage. I'm starting to think that this could be a useful indicator of how well your flights are doing and which ones to scale up to full torque - before, I wouldn't have been able to tell which settings between Flight 7 and Flight 8 to stick with as my trim (obviously both of them aren't optimized and I'm still in the trimming process) but now I know that Flight 7 was much more inefficient.

I'm also in the process of rechecking my plane configuration ahead of a potential extended session tomorrow and I found that my HS tilt and wing warp have changed from me carrying the plane back and forth from the school. My wing warp increased from 0.6 cm to 1.1 cm (nearly 4x the recommended value) and my HS tilt from 0.7 cm to 1 cm. Is there any way I can prevent these from changing so much besides being more gentle with the plane? Am I not putting enough glue on the joints?

I've added the videos for my latest flights if the coaches want to check them out. Planning to fly at full torque tomorrow and potentially moving to different rubber densities.

Thanks for all the help so far,
Astro

Astro,

It's good that you are checking your trim parameter measures. We check them every time we fly. There is more I can write on your question of parameter changes, but it's late and there is actually a different key testing change I would recommend. I see from your log that you have quite a large number of turns remaining at the end of most flights. This is an indicator that the rubber you are using is too thin. Move to the next thicker rubber in the kit for your next tests and you should see longer flight times. Remember that thicker rubber will most likely climb stronger and will need to be tested initially at much lower launch torque, more backoff turns (like 0.3 in oz launch torque after a wind up of at least 1.0 in oz).

A rule of thumb for a good number of turns remaining is to be equal to the number of backoff turns. See the winding specs for my 2023-24 Super Simple Flight Airplane video here and notice the number of max turns, max torque, backoff turns, launch torque and turns remaining. The flight in the video was the third or fourth flight of that day with the other flights launched a much lower launch torque (all wound to nearly the same max turns and max torque though.) https://www.youtube.com/watch?v=bXUgm4LQn1s&t=1s This flight video and a build video for this 2023-24 Super Simple airplane are both also on the new 2023-24 NFFS SO website. This airplane takes 1/2 hour to build out of craft store balsa with grocery bag covering (costs about $10) and you'll see that, with proper winding and propeller matching to the rubber it flies over two minutes (this is an undersized Div B airplane, but could be slightly resized smaller for Div C and would fly about the same).

Brian T

[coachchuckaahs]

Flying opportunity: https://www.indoorffsupply.com/events

This is an AMA contest. Juniors (18 and under) are $35, and this includes an AMA membership if needed.

This is a high ceiling site, about an hour north of Austin TX. The ceiling is close to 100 feet! Experts including Dave Lindley, Coach Chuck, and others will be there to help. Science Olympiad planes are welcome, any year version. Get help trimming, winding, and improving! I know it is early in the new SO year, but bring last year's plane and learn!

Coach Chuck

[Astronomyguy]

What thickness balsa is best for making props? I’m not planning to do so right now but I’m giving me team members who are planning to do wind power and tower some of my balsa from last year, and I’m not sure which sizes to keep for balsa props.

[bjt4888]

What thickness balsa is best for making props? I’m not planning to do so right now but I’m giving me team members who are planning to do wind power and tower some of my balsa from last year, and I’m not sure which sizes to keep for balsa props.

Astro,

1/32” thick sheet works well. We’re use 6-7.5 lb cu ft density C-grain. A-grain is fine too if you want a little softer flaring from the blade. If you don’t have any 1/32” of the right density or grain you can “thickness sand” some 1/16” down to 1/32”. See The NFFS prop building video for the trick to sanding to specific thickness.

Brian T

[coachchuckaahs]

What thickness balsa is best for making props? I’m not planning to do so right now but I’m giving me team members who are planning to do wind power and tower some of my balsa from last year, and I’m not sure which sizes to keep for balsa props.

I agree with Coach Brian here. No need on SO to sand thinner than 1/32". Use A grain with caution, it is easy to over-flare and not climb at all. As long as the density is 7-8# A grain should be ok. C grain down to 6# is fine, though probably not necessary. We generally use 7.75# C grain to start with.

It is better to vary the flare by adjusting the rotational stiffness of the spar. If a wood spar, sanding will reduce stiffness. If carbon, the length of exposed spar from the hub to the blade is your adjustment. If too soft, add some small scraps of balsa between the carbon rods.

Coach Chuck

[coachchuckaahs]

Texas Event Results:

Two SO teams flew at the Belton TX AMA event, one Saturday and one Sunday. I worked directly with the team on Sunday.

While the ceiling was 90 feet, they chose to work at 25 feet to simulate their upcoming event (invite).

Initial flights were about 1.5 minutes (Div B). Final flights were about 2.5 minutes, with room for even more improvement. I wanted to report the findings here because they are VERY TYPICAL of what we see when we help teams.

1. Initial flights were flat and fast. While the plane climbed, it raced a lot, using up turns of rubber fast. The wing was mounted with 0 incidence. The team added incidence with shims until the plane stalled, and then removed a little. End incidence was about 6mm.
2. After trimming, the plane climbed too much. A significant impact was about 1cm of left wing wash-in. This is excessive. After several adjustments, they ended up at 0 wash-in, and the plane still did not roll in on high torque (torque enough to reach 65 feet). The needed wash-in may vary with kit makers, but this one (J&H) flew fine without wash-in. Extra wash is drag!
3. The students were winding UP to launch torque. We taught how to wind to near breaking and back off to launch torque. This was a huge increase. In addition, they reduced launch torque until the plane climbed only to 25 feet. "Near Breaking" was not actually obtained. They had difficulty winding above about 1.2 oz-in because the winder got stiff. Some lube (petroleum jelly or lithium grease) in the winder may help. But going to 1.0-1.2 and backing off left far more winds in the rubber than simply winding up to launch torque.
4. Rubber selection: They had three "widths" of rubber, 0.079", 0.085", and 0.093" I believe. After all of the trimming, the two heavier widths resulted in no letdown prior to running out of turns, while the lightest (0.085) resulted in too many turns (full row of knots) remaining. At this point, two choices: Adjust the prop pitch (slightly more pitch and use the 0.085) or get new rubber. I cut some of my stock to 0.088, and this was way too strong. We ended up around 0.083" with my rubber. The difference? My rubber batch was probably substantially thicker than that supplied with the kit. This happens batch-to-batch and within a batch. This is why it is important to measure the linear density (g/in) or loop length (before any winding) rather than the width of the cut rubber.
5. Logs" While the rubber selection, winds, unwinds, and torque were recorded, it is also important to capture the trim parameters (wing incidence, CG location, wash-in, etc.). This may not affect your one best flight, but it will allow you to further experiment at your next session with the same starting point, and to know what you have already tried and adjusted
6. Ongoing: Test CG location, moving small amounts back or forward while re-trimming for optimal flight; Test various prop pitches, re-optimizing rubber selection each time, and adjusting launch torque for 25 feet peak altitude; Test various props, within limitations of the measuring box.

I hope this experience helps others. While I cannot share exact details of the team's findings, the trends are identical to most teams that have a flying plane but want to do better. Resources for improving can be found at the NFFS web site, https://www.freeflight.org/science-olympiad/, click on Student Resources button. Basic trimming and rubber winding are highlighted in the flying tab.

Coach Chuck

[FlyingPie]

Hi everyone!

First post on this forum,

I wondered if you guys had any suggestions for winding procedures for low-flight venues. Tryouts for the team at my school has flight tryouts happening in a 15 Ft space (Cafeteria), which is not something that I am normally used to flying (I have been flying at my local gym). I have been following the procedure of using backoff winds to get to my launch torque, but my plane still launches into the air, and even in a full-sized gym, it usually touches the rafters multiple times. I think that it may have something to do with the decalage, but not totally sure where it is coming from. My wing incidence is currently in the sweet spot (If I move it down, there is no climb, up, and it stalls), and I think that my CG is relatively okay.

I am using .87 rubber,

Thank you guys for all the information that you have in these forums!